Is using letter outside our native alphabet consided offensive?

I didn't know what flair to put this under. As a disclosure I'm British and I suck at learning languages but this annoyed me so I made up my own fake language and a pretend island to go with it. It's nice to just close my eyes and pretend to be on a island on my own way from bad things and some of the letters have (what I understand to be called accents but I'm I'm wrong please correct me) to make it feel more not english (sorry if this is sounding bad in anyway I'm not best with words). I like to write story's with some if the charecters with these letters like ā, ķ, ï and other letters like that but if I were to change my name to somthing with a lette like ē in it would that be consided offensive?